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HL: Halbleiterphysik

HL 63: Ultrakurzzeitph
änomene

HL 63.8: Vortrag

Mittwoch, 9. März 2005, 12:30–12:45, TU P-N201

Dynamic polarization filtering in strained M-plane GaN films — •T. Flissikowski¹, K. Omae¹, P. Misra¹, O. Brandt¹, H. T. Grahn¹, K. Kojima², and Y. Kawakami² — ¹Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin, Germany — ²Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan

We have observed dynamic polarization filtering in anisotropically strained M-plane GaN films on γ-LiAlO₂. The in-plane polarization anisotropy, resulting from the anisotropic strain, leads to a static polarization filtering due to the much larger absorption coefficient for light polarized perpendicular to the c-axis α_⊥ in comparison to α_∥ [1,2]. In order to investigate dynamic polarization filtering in these films, a polarization sensitive, femtosecond pump-and-probe technique is used in connection with a micro-optical setup in order to bleach α_⊥. In this case, the effective static polarization rotation of the probe toward the c-axis can be almost canceled by the pump pulse. The amplitude of this dynamic filtering strongly depends on the photoexcited carrier density as well as on the hole redistribution between the upper two valence bands. The time scale of this dynamic filtering is mostly determined by the carrier recombination time. Furthermore, the pump-induced changes in α_⊥ and α_∥ can also alter the refractive indices n_⊥ and n_∥. Consequently, the ellipticity of the outgoing light beam is investigated during dynamic filtering.

[1] P. Misra et al., Appl. Phys. Lett. 83, 4327 (2003).

[2] P. Misra et al., J. Appl. Phys. 96, 1. Dec. (2004).